Segmenting Stream Files

Sometimes, when your disc has content that requires two layers, you cannot find a way to lay out your files so that neither layer is too large. This happens when you have very large transport files (XXXXX.m2ts). In particular, if you have any single file that’s larger than about 12 million sectors, it won’t fit onto a single layer.

Under these circumstances, it is possible to split a file across the two layers, but the difficulty comes in finding a good place within the file to use as the split point. Because the layer change takes time in a hardware Blu-ray player, you don’t want the split point to occur in the middle of a scene.

With Tracer, you can use the playback window to find a good split point visually, then lay out your files with the layer break between the segments of the split file.

To begin, use the playback window to start playing the clip that you wish to divide. When it is playing, click Freeze at the bottom of the playback window — you don’t want playback to end while you are busy choosing your split point:

In the bottom left corner, next to the Eject button, you’ll see a small gray “disclosure” triangle. Click it to expand the window to reveal the hidden controls you’ll use to create a split point:

At the bottom center of the window, you’ll now see a sector number, which is the approximate position of the current frame within its transport stream file.

Remember that the locations and sizes of files in the Files tab are given in terms of sectors.The position is approximate because a frame may fit entirely within a sector, or it may be split across two sectors, or it may require multiple sectors.

Amongst the newly revealed controls, you’ll see there are three pairs of frame navigation tools:

• Single-frame Forward and Backward buttons. Use these buttons to navigate the clip one frame at a time.
• Splittable-frame Forward and Backward buttons. Not every frame is allowable as a split point. Use these buttons to navigate between allowable split points.
• Segment Forward and Backward buttons. Since the clip in our example hasn’t been split yet, it consists of a single segment.

You can also drag the time code slider above the sector number display to go directly to different positions within the clip.

There is a second (non-draggable) slider below the sector number, which visually represents the position of the current frame’s sector within the transport stream file.

The last pair of buttons are the Split and Join buttons, which you’ll make use of soon. Note the text above these buttons: the clip number of the current clip, its play item number and its playlist number. In our example, there is only one play item, so it’s number 0.

Let’s compare this information with what’s shown in the Files tab of the job window:

The layer break is highlighted in the list, and above it is the transport stream file for clip 2. It’s quite small, only about 150,000 sectors, but we’re going to split it anyway, as a demonstration of the technique.

If you look back at the playback window, you’ll see that the current frame is at sector 86,085 of the clip file, a little over halfway through. Considering where we paused playback, that looks about right.

In terms of dividing the stream file, this might seem like a potential split point. But you can tell from watching the video that we’re in the middle of a steady shot, so this is actually not a good place to put the layer break. By scrubbing around a little using the time code slider, you can find a place nearby where the video cuts from one shot to another:

Let’s use that as the split point. All you need to do is click the Split and Split button, and notice what changes in the window:

Since you have started a new segment at the current position, playback now at sector number 0 within the new segment, which is segment #2. (The part of the file before the split point is segment #1.)

Let’s look at the Files tab again, and see what’s changed there:

The two segments of stream file 00002.m2ts now appear as separate entries in the list. To place the layer break between them, just drag it into position and you’re done: